That is a good price if they are going to do all of the removal and install. My guy (Anthony) will do black basic LineX for 600 if you drop it off. If you want LineX extra (any color, UV protectant) it was 750-800.
I don't know how to define specialist. All LineX dealers are franchise owners. They have very strict rules they have to follow and you certainly cannot do it yourself. It takes very special equipment, a spray gun with more than one nozzle, heated to 160 degrees IIRC, sprays out at 2500lbs of pressure. LineX is actually a two part material, hardens within seconds of leaving the nozzle.

As for the interior, I can get some pics I have no carpet left inside, herculined the entire horizontals of the interior. Multiple coats. Basically, I used several of the medium sized cans they offer. No more interior rust, no more worrying about mud stains!

I still need to get some LEDs to do the gage face swap.